Method and composition for treating low-temperature subterranean formations

ABSTRACT

A water-insoluble particulate composition having controlled oil solubility is disclosed. This composition is comprised of solid particles of a homogenous mixture of (1) about 10 to 13 weight percent of an ethylene-vinyl acetate copolymer that contains about 23 to 30 weight percent vinyl acetate and exhibits a melt index of about 300 to 500 grams per 10 minutes and (2) a paraffin wax that contains at least 70 weight percent hydrocarbons having 25 to 32 carbon atoms per molecule. Also, a process employing this particulate composition in drilling wells into lowtemperature subterranean formations, and in fracturing and treating such formations, is disclosed.

United States Patent Inventors Appl. No. Filed Patented Assignee METHODAND COMPOSITION FOR TREATING LOW-TEMPERATURE SUBTERRANEAN FORMATIONS !9Claims, No Drawings US. Cl 166/283, 166/295, 175/72, 252/85, 252/855Int. E2"! 33/138, E2lb 43/26 Field of Search 166/281- 283, 295, 308;l75/72; 252/85 LC, 8.55

Primary Examiner-Ian A. Calvert Attorneys-Milton W. Lee, Richard C.Hartman, Lannas S.

Henderson, Dean Sandford and Robert E. Strauss ABSTRACT: Awater-insoluble particulate composition having controlled oil solubilityis disclosed. This composition is comprised of solid particles of ahomogenous mixture of 1) about 10 to l3 weight percent of anethylene-vinyl acetate copolymer that contains about 23 to 30 weightpercent vinyl acetate and exhibits a melt index of about 300 to 500grams per 10 minutes and (2) a paraffin wax that contains at least 70weight percent hydrocarbons having 25 to 32 carbon atoms per molecule.Also, a process employing this particulate composition in drilling wellsinto low-temperature subterranean formations, and in fracturing andtreating such formations, is disclosed.

METHOD AND COMPOSITION FOR TREATING LOW- TEMPERATURE SUBTERRANEANFORMATIONS This invention relates to well drilling and treating, andmore particularly to a composition and method for temporarily reducingthe permeability of low-temperature, permeable oilbearing formations.The method and compositions of this invention have particularapplication in hydraulic fracturing, in

well treating and in completing oil and gas wells that penetratelow-temperature formations.

Although high fluid permeability is a desirable characteristic ofhydrocarbon producing formation, many drilling, fracturing andwell-treating operations are adversely affected when a well penetratessuch highly permeable formations. The effectiveness and efficiency ofthese processes are substantially improved by plugging the morepermeable strata to reduce the loss of drilling, fracturing, andwell-treating fluids thereto. Accordingly, low fluid loss agents havebeen developed for use in these applications. Also, particulate pluggingagents are used as diverting agents in multiple fracturing operations,and to plug selected strata to obtain fluid shutoff.

In the aforesaid applications, it is essential that the temporary fluidloss control or plugging agent .be readily removed from the hydrocarbonproducing zones to prevent permanent loss of permeability and anattendant reduction in oil production rate. Removal may be effectivelyaccomplished by utilizing an agent that is soluble in the formationhydrocarbons. However, many of the prior art materials are eitherinsoluble under bottom hole conditions, or are so highly soluble thatthey are difficult to place in the formation and fail to maintain therequired plug during the treating operation. It is therefore es sentialthat the fluid loss or plugging agent possess the property of controlledsolubility, wherein a satisfactory solid plug will be formed for aperiod of time, and whereupon the plug will be removed by being slowlydissolved by the formation hydrocarbons.

It is also advantageous to utilize a material that is insoluble inwater, thereby leaving any water producing strata permanently sealed.Thus, a selective plugging is effected, the hydrocarbon producing stratabeing temporarily plugged and the water producing strata remainingpermanently plugged. On removal of the temporary plugging agent from thehydrocarbon-producing strata, oil and gas production capability is fullyrestored, while water production is permanently eliminated orsubstantially decreased.

Each of the aforesaid well treating processes commonly require atemporary plugging material capable of being formed into small solidparticles of controlled size, preferably by an inexpensive technique.The material should be slowly soluble in the formation hydrocarbons andinsoluble in water at formation conditions to accomplish the desiredselective plugging and complete restoration of hydrocarbon permeability.Particle size is important in controlling the distance that the pluggingagent penetrates into the formation and the degree of fluid shutoffobtained. Therefore, it is essential that the particles do notagglomerate or stick together in the treating fluid during the treatingoperation. While other properties of the particulate agent may influenceparticle agglomeration, agglomeration is largely controlled by thetackiness of the particle surface. Hence, it is necessary that thevplugging particles or agents exhibit a low degree of tackiness onexposure to air at ambient temperatures and also remain nontacky or nonsticky upon exposure to formation hydrocarbons and to the treatingfluids. In addition, particles which are somewhat resilient possesssuperior plugging properties, since they deform to effectively fill flowpassages. Also, high mechanical and impact strength is desirable toavoid size reduction of individual particles by attrition.

Various slowly oil-soluble, water-insoluble particulate agents useful inwell drilling and treating operations have been developed. Inparticular, U.S. Pat. No. 3,316,965 discloses the use of homogeneoussolid particles of nongaseous hydrocarbon and polymer; U.S. Pat. No.3,342,263 discloses the use of discrete solid particles of a homogeneoussolid mixture of a polymer and a halogenated aromatic hydrocarbonmelting above about F., U.S. Pat. No. 3,363,690 discloses solidparticles comprised of a homogeneous mixture of polymer, wax, and resin.While these compositions are satisfactory in many well drilling andtreating applications, and their use has contributed greatly toincreased oil recovery, they have not been completely successful in thetreatment of relatively lowtemperature subterranean formations.

The bottom-hole temperature of a well varies with the geographicallocation of the well and with its depth. Many producing wells,particularly in the United States and Canada have bottom-holetemperatures under I25 F., and often as low as 90 F. and below. In orderthat the treated wells can be returned to full production, the injectedtemporary plugging or diverting agents must be soluble in the reservoiroil at the reservoir temperature to the extent that substantially all ofthe plugging agent is removed within a reasonably short time, such asbetween about 1 and 6 days after returning the well to production. Thesolid compositions that are completely solubilized by the reservoir oilin less than l2 hours or greater than 6 days have been found to beundesirable for many of the welltreating processes. Many of thecompositions disclosed in the foregoing patents, while quitesatisfactory for the treatment of formations having temperatures aboveabout F., are not sufficiently soluble at lower temperatures to provideoptimum treatment of the lower temperature formations, and particularlythose formations having temperatures of 90 F. and below, or do notpossess the requisite properties of strength and nontackiness. Thus,there exists a need for a particulate solid composition that is slowlysoluble in oil at low formation temperatures, that is insoluble inwater, and that exhibits other requisite properties of hardness,strength and nontackiness.

Accordingly, it is an object of this invention to provide an improvedwell-treating process for temporarily plugging lowtemperaturesubterranean formations. Another object of the invention is to providean improved well-treating process for plugging or retarding fluid flowthrough low-temperature earth formations that does not permanentlyreduce the permeability of the formation to hydrocarbon fluids. Anotherobject of the invention is to provide a process for fracturinglow-temperature subterranean formations wherein a diverting agent isdeposited in the fracture to retard the flow of fracturing fluid thereinand to effect multiple fractures in the formation. Another object of theinvention is to provide an effective low fluid loss additive foraddition to a fracturing fluid. A still further object is to provide alow fluid loss additive to be added to a fluid placed in a well borepenetrating a low-temperature formation which will act to temporarilyreduce the formation permeability without effecting a permanentreduction of the hydrocarbon permeability of the formation. A stillfurther object is to provide a fluid loss additive which is soluble uponprolonged contact with low-temperature reservoir hydrocarbons and thatremains nontacky when incorporated into a treating fluid. Other objectsand advantages of the invention will be apparent to those skilled in theart from the description thereof which follows.

The foregoing objects and their attendant advantages can be attained bytreating the subterranean formation with a particulate materialcomprising solid particles of a homogeneous mixture of I) about 10 to 13weight percent of an ethylenevinyl acetate copolymer that contains about23 to 30 weight percent vinyl acetate and exhibits a melt index of about300 to 500 grams per 10 minutes and (2) paraffin wax that contains atleast 70 weight percent hydrocarbons having 25 to 32 carbon atoms permolecule. The particulate composition is insoluble in water and slowlysoluble in oil, and is particularly useful as a fluid loss control agentand as a diverting or plugging agent in treating and hydraulicallyfracturing a lowtemperature subterranean earth formation penetrated by awell, and in drilling a well into such formations.

The oil solubility of the particulate composition is determined byintimately contacting the particles with liquid hydrocarbon, such ascrude petroleum recovered from a lowtcmperature formation to be treated,maintained at the temperature of the formation. The particulatecompositions of this invention are slowly soluble in oil at atemperature of 125 F., yet are completely soluble on prolonged contactwith the oil at a temperature of 90 F. Preferably, the particulatecomposition is relatively insoluble on contact with oil for a periodsufficient to complete the particular treating operation, and completelydissolved or dispersed in the oil at the termination of the treatment.Thus, a particulate composition useful in treating a wide range oflow-temperature fonnations is substantially insoluble on contact withoil at a temperature of 125 F. for a short period of time, and iscompletely dissolved or dispersed in the oil so that no solid residueremains to plug the oil-bearing strata of the formation after contactingthe formation for a prolonged period.

The particulate compositions of this invention exhibit a low degree oftackiness on exposure to air at ambient temperatures and also remainrelatively nontacky upon exposure to formation hydrocarbons and to thetreating fluids with which they are contacted. Hence, the particles tendto remain as discrete solid particles and do not agglomerate eitherduring storage or during use in a treating operation.

Tackiness value is a relative indication of the tackiness ofaparticulate composition, and can be determined by a standardized beadadhesion test. In this test, the molten composition to be tested iscooled to 200 F. and dropped onto a horizontal stainless steel plate atambient temperature using a standard medicine dropper having a 1/l6-inchorifice held 1 inch above the plate. After standing for 5 minutes atroom temperature, the solidified beads are removed from the plate. Thetackiness value is determined by the tenacity with which the beadsadhere to the plate, and is rated as follows:

Tackiness Value Degree of Adhesion Intermediate tackiness values areestimated based on the proportion of beads falling into two or more ofthese categories.

The particulate compositions of this invention exhibit tackiness valuesdetermined in accordance with the above techniques of 1.0 or less, andpreferably exhibit tackiness values of 0.5, or below.

The particulate compositions which exhibit the desired properties ofslow oil solubility and low tackiness value are solid particles of ahomogeneous mixture comprising (1) about to 13 weight percent of anethylene-vinyl acetate copolymer having about 23 to weight percent vinylacetate and exhibiting a melt index of about 300 to 500 grams per 10minutes, and more preferably about 335 to 465 grams per 10 minutes, and(2) a paraffin wax containing at least 70 weight percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.

A particularly preferred polymer for use in the composition of thisinvention is an ethylene-vinyl acetate copolymer that contains about 24to 26 weight percent vinyl acetate and exhibits a melt index of about335 to 465 grams per 10 minutes. A commercial ethylene-vinyl acetatecopolymer exemplary of this preferred copolymer is marketed by E. l.duPont de Nemours Company under the trademark Elvax 310.

Another preferred polymer is an ethylene-vinyl acetate copolymer thatcontains about 27 to 29 weight percent vinyl acetate and exhibits a meltindex of about 335 to 465 grams per 10 minutes. A commercialethylene-vinyl acetate copolymer exemplary of this preferred copolymeris marketed by E. l. duPont de Nemours Company under the trademark Elvax210.

The term melt index" as employed herein is the flow rate reported as therate of extrusion in grams per 10 minutes as determined by ASTM testmethod D1238-65T entitled Measuring Flow Rates of Thermoplastics byExtrusion Plastometer" and performed under Standard Test Condition E,ASTM Standards, American Society for Testing and Materials, Part 27,June, 1969, pages 455466, which procedure is herein incorporated byreference.

The wax employed in the particulate composition of this invention is acrystalline paraffin wax that contains at least 70 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule, and morepreferably the wax is a fully refined crystalline paraffin wax. The oilsolubility of the particulate composition depends in part on theproportion of hydrocarbon molecules of different carbon chain lengths,i.e., the proportion of hydrocarbons having a different number of carbonatoms per molecule, in the wax. We have found that wide-cut waxescontaining hydrocarbons of different carbon chain lengths produce aproduct of lower oil solubility than the more narrow-cut waxescontaining hydrocarbons having a more limited number of carbon chainlengths. In particular, the waxes useful in the compositions of thisinvention contain at least about 70 weight percent hydrocarbons having25 to 32 carbon atoms per molecule, and more preferably contain at leastabout weight percent hydrocarbons having 25 to 32 carbon atoms permolecule. These waxes exhibit melting points of about 138 F. to 145 F.,and more preferably of about 140 F. to 142 F. However, melting pointalone is not indicative of the carbon chain length or the number ofcarbon atoms per molecule since the melting point of a wide-cut waxfraction containing hydrocarbons of many different chain lengths may bethe same as that of a narrow-cut fraction.

The compositions of this invention are readily prepared by melting theindividual components and then admixing the molten liquids in the properproportions. Alternatively, the solid ingredients can be combined in theproper proportion and then melted to obtain a homogeneous liquidmixture. In either case, the proportion of each component is selected toimpart the desired properties to the final solidified product.Compositions suitable for treating low-temperature subter raneanformations contain between about 10 and 13 weight percent of theaforementioned ethylene-vinyl acetate copolymers, and preferably betweenabout 10 and 12 weight percent copolymer, with the balance of themixture comprised of the aforesaid wax. Also, the compositions cancontain minor proportions of additives, such as oxidation inhibitors,etc.

A particularly preferred particulate composition comprises solidparticles ofa homogeneous mixture of l about 10 to 13 weight percent ofan ethylene-vinyl acetate copolymer that contains 24 to 26 weightpercent of vinyl acetate and exhibits a melt index of about 335 to 465grams per 10 minutes and (2) about 87 to 90 weight percent of a fullyrefined crystalline paraffin wax containing at least about 90 weightpercent hydrocarbons having 25 to 32 carbon atoms per molecule.

Another preferred composition comprises solid particles of a homogeneousmixture of 1) about 10 to 13 weight percent of an ethylene-vinyl acetatecopolymer that contains 27 to 29 weight percent of vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes and (2)about 87 to 90 weight percent of a fully refined, crystalline paraffinwax having at least about 90 weight percent hydrocarbons containing 25to 32 carbon atoms per molecule.

The solid particles used in the practice of this invention vary widelyin size and shape. Typically, these particles can be speroids, cubes,granules, buttons, flat discs, or mixtures thereof, having meandiameters in the range of from about one-half la. M.

inch to about 1 micron and less More particularly, -the particles can becubes, buttons. or discs having mean diameters from about one-eighthinch to about one-half inch. speroids or granules in the size range offrom about 4 to 200 mesh U.S. standard screen, or particles having meandiameters from about 1 to 50 microns.

The composition of this invention is useful in treating lowtemperaturesubterranean formations having temperatures of l25 F. or less, and isespecially useful in treating formations having temperatures of l00 F.or less, and in many instances in the treating of formations havingtemperatures of 90 F. or less. In its broadest application, the processcomprises contacting a subterranean formation penetrated by well with asuspension of solid particles of the aforesaid composition in a suitablecarrier liquid injected through the well. This treatment can comprise asingle temporary and selective plugging step, or it can be an integralpart of a comprehensive fracturing, well drilling, acidizing, or solventtreating process. Also, the particulate composition of this inventioncan be effectively used as a low fluid loss agent in a drilling fluidemployed in well drilling and particularly as a low fluid loss agent. incompletion fluids employed in thedrilling of oil and gas wells, and inworkover fluids employed in recompleting oil and gas wells. In thedrilling and workover applications, the drilling fluid is circulatedfrom the surface to thedrilling zone in a low-temperature formationduring the drilling operation, and at least a portion of the fluid isreturned to the surface. The particulate compositions of this inventioncan be incorporated in the fracturing fluids employed in hydraulicallyfracturing an earth formation surrounding a well, and the compositioncan be employed in chemical treating, acidizing, and other welltreatingoperations wherein it is desired to control fluid loss to permeableunderground structures.

The particulate compositions of this invention can be more readilydispersed into a carrier liquid by the addition of a small amount of asurface-active agent to the carrier liquid. Also, small amounts of asurface-active agent or a mixture of surinvention, and are not intendedas limiting the scope of the invention as defined by the appendedclaims.

EXAMPLES l-l9 The criticality of the particular ethylene-vinyl acetatecopolymer and paraffin wax employed in preparing the compositions ofthis invention is illustrated by this series of examples. In eachexample a particulate diverting agent composition is prepared byadmixing 10 weight percent of various molten ethylene-vinyl acetatecopolymers marketed by the E. I. duPont de N emours Company under thetrademark Elvax and about 90 weight percent of various paraffin waxes.The tackiness of the various compositions is determined in the mannerheretofore described, and the compositions are formed into soliddiverting agent particles.

The oil solubilities of solid particles of the various compositions aredetermined by placing four 3/ 16-inch diameter particles of each of thevarious compositions in each of six 6-dram vials. Two of the vialscontaining each composition are separately filled with a 39.6 API crudeoil from the Reagon field, Montana; two of the vials are filled with a429 API crude oil from the Graylin field, Michigan; and two of the vialsare filled with a solvent comprised of volume percent kerosene and 30volume percent neutral oil (a paraffinic lubricating oil having aviscosity of about 90 SUS at 100 F.). One set of three vials containingone vial of each of the solvents is placed in an oven maintained at F.and rotated at approximately 16 rpm. for about 6 days, and the other setof three vials is placed in an oven maintained at 90 F. and similarlyrotated. At the end of the 6-day period, the vials are removed from theoven and the contents poured over a mesh U.S. standard screen and thescreen examinedifor solid particles. The compositions leaving traceamounts or more of particles on the screen after exposure to any of thethree solvents are deemed insoluble, and the compositions leaving nodetectable solid residue on the screen are deemed soluble.

The results of these tests are reported in table 2.

TABLE 2.-SOLID WAX/ETHYLENE-VINYL ACETATE COPOLYMER COMPOSITIONS ANDTHEIR PROPERTIES copolymer Properties VA 2 Melt Wax content index 3Solubility 5 wt. (g./10 25-32 CN 4 Example Trademark l percent min.)Supplier Trademark wt.percent Tackiness at 95 F. at 90 F.

Elvax 40 39-42 45-70 Union Oil Co. of California- Aristowax 94 1.0 SElvax 210 27-29 335-465 do 0 94 0.2 S S Elvax 220. 27-29 125-175 94 0. 2I I Elvax 310. "4-26 335465 94 0. 2 S I Elvax 410... 1749 430-580 0 940.2 I I Elvax 210 27-29 335-465 91 0. 5 S S Elvax 220. 27-20 125-175 910.5 I 1 Elvax 310 24-26 335-465 91 0.2 S I Elvax 410. 17-19 430-580 .do91 0.2 I I Elvax 210 2729 365465 Cities Service Co. 82 0.5 S I Elvax220. 27-29 125-175 d0 82 0.5 I I Elvax 310. 24-26 335-465 do. 82 0.2 S IElvax 410. 17-11 430-580 .....d0 82 0.2 I I Elvax 210. 27-29 335-i65I'nion Oil Co. of California- 71 0. 2 S I Elvax 220... 27-29 125-115 d071 0,5 I I Elvax310... 24-26 335-465 ..do.. 71 0 S I Elvax 410.. 17-19430-580 d0. 71 0 I I Elvax 210 27-29 .dO 58 0. 2 I I 19 ..Elvax3l0....24-26 335580..... 58 0.2 I I 1 Elvax copolymers are marketed by E. I.duPont de Nemours Company.

1 Vinyl acetate content of the ethylene-vinyl acetate copolymer. 3 MeltIndex as determined by ASTM D123865T.

4 Content of hydrocarbons in was having 25 to 32 carbon atms permolecule.

5 The symbol S means soluble and the snnbol I means insoluble.

As shown in table 2, the compositions that are soluble in all threesolvents at 95 F. are comprised of mixtures of (l) ethylene-vinylacetate copolymers that contain 24-,29 weight percent vinyl acetate andexhibit a melt index of 335 to grams per 10 minutes and (-2) paraffinwaxes containing at least 71 weight percent hydrocarbons having 25' to32 carbon atoms per molecule; and the compositions that are soluble at90 F. contain paraffin waxes having at least 91 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule The data reportedin table 2 further illustrate the effect of the ethylene-vinyl acetatecopolymer composition on the solubility and tackiness of thewax-copolymer product Example 1. for instance, shows that copolymershaving high vinyl acetate contents and low melt indexes render theproduct too tacky, while examples 5,9, 13 and 17 illustrate thatcopolymers with low vinyl acetate contents adversely affect thesolubility of the wax-copolymer product.

EXAMPLE 20 A diverting agent composition is prepared by admixing l) 12weight percent of a molten ethylene-vinyl acetate copolymer containingabout 24 to 26 weight percent vinyl acetate and exhibiting a melt indexof about 335 to 465 grams per minutes, (2) about 87.9 weight percent ofa molten paraffin was that has a melting point of about 140 to 142 F.and contains about 94 weight percent hydrocarbons having 25 to 32 carbonatoms per molecule, and (3) 0.1 weight percent of 2,6-ditertiarybutylpara-cresol, an oxidation inhibitor. The ethylene-vinyl acetatecopolymer is marketed by the E. l. du- Pont de Nemours Company under thetrademark Elvax 310. The wax is a fully refined, crystalline paraffinwax marketed by the Union Oil Company of California under the trademarkAristowax 1408.

The molten wax-copolymer composition is formed into discrete solidparticles of the following size ranges:

1. Flat buttons havi g a thickness of approximately one-sixteenth inchand a diameter of about one-fourth inch to threeeighths inch;

2. Particles having sizes in the range of about 8 to 100 mesh U.S.standard screen; and

3. Particles having sizes in the range of about 1 micron to 100 meshU.S. standard screen.

Approximately 50 percent of the particles in the 8 to 100 mesh sizerange have sizes in the range of 8 to mesh U.S. standard screen andabout 50 percent have sizes in the range of 20 to 100 mesh.

EXAMPLE 21 This example illustrates the use of the method andcomposition of this invention in treating a low-temperature,subterranean, oil-containing reservoir to stimulate the recovery of oiltherefrom. The well is completed in a relatively shallow reservoirhaving a temperature of 90 to 95 F., with a total productive interval of10 feet perforated with two holes per foot at the depths of 3,066 to3,072 feet and 3,082 to 3,086 feet.

The stimulation treatment is performed by injecting 3,000 gallons of 15percent hydrochloric acid into the well, then in troducing 12 pounds ofparticulate diverting agent, and then injecting another 3,000 gallons ofacid. The diverting agent comprises flat buttons approximately onefourthinch to threeeighths inch in diameter of the slowly oil-soluble,water-insoluble homogeneous solid composition described in example 20.The initial slug of acid is injected into the well under vacuum.However, the second slug of acid injected after treatment with thediverting agent particles is injected at a surface pressure of 1,100p.s.i.g.

Upon completion of the acid injection, the well is flushed with leasecrude and then with water, and the well returned to production. Theproduction rate of oil is observed and found to be substantially higherthan the rate prior to the stimulation treatment, which indicates thatthe stimulation treatment is successful and that the diverting agentparticles are substantially removed from the oil-producing zones.

EXAMPLE 22 This example illustrates the use of the method andcomposition of this invention in fracturing a low-temperature,subterranean oil-producing formation A production well is completed in arelatively shallow reservoir having a tempera ture of 90 to 95 F., witha total productive interval of 15 feet perforated with two holes perfoot at the depths of 2,903 to 2,908 feet and 2,918 to 2,928 feet.

Fracturing is accomplished by injecting 10,000 pounds of 20 to 40 meshsand in 10,000 gallons gelled brine into the well at a volume flow rateand pressure sufficient to fracture the formation. After approximatelyone-half of the fracturing fluid is injected, 10 pounds of divertingagent particles are slugged into the well and the fracturing fluidinjection continued. The diverting agent comprises flat buttonsapproximately onequarter inch to three-eights inch in diameter of theslowly oilsoluble, water-insoluble homogeneous solid compositiondescribed in example 20. The initial portion of the fracturing fluid isinjected at a surface pressure of 950 p.s.i.g. However, the injectionpressure is increased to 1,500 p.s.i.g. after treatment with thediverting agent.

Upon completion of the fracturing operation, the well is flushed withlease crude and returned to production. The production rate ofoil isobserved and found to be substantially higher than the rate prior tofracturing, which indicates that the fracturing operation is successfuland that the diverting agent particles are substantially removed fromthe oil-producing zones.

EXAMPLE 23 This example illustrates the use of the method andcomposition of this invention in drilling a well into a low-temperatureformation having a temperature of to F. This well had previously beendrilled to a depth of 3,108 feet and then plugged to a depth of 2,924feet with pea gravel and cement. For a number of years the well wasproduced from a productive interval from 2,911 to 2,922 feet. However,it is now desired to open lower zones to production.

The plug is drilled out using a 3%-inch-diameter bit on a conventionaltubing string. Brine is used as a drilling fluid, and is circulated fromthe surface to the drilling zone and returned to the surface. The wellis drilled from 2,924 feet to 3,005 feet without incident, butcirculation is lost to the formation at 3,005 feet. Approximately 750pounds of diverting agent particles are added to a gelled brine and thedrilling resumed using this material as the drilling fluid. Thediverting agent comprises particles of the slowly oil-soluble,water-insoluble homogeneous solid composition described in example 20,the particles having sizes in the range of 8 to mesh U.S. standardscreen, with approximately 50 percent of the particles having sizes inthe range of 8 to 20 mesh and 50 percent having sizes in the range of 20to 100 mesh. After addition of the diverting agent, good fluidcirculation is observed. Drilling is continued to a depth of 3,108 feetwithout further difficulty.

The gelled brine is displaced from the well with ungelled brine, andagain the formation did not take fluid. Then, 14 barrels oflease crudeis placed in the well and allowed to stand overnight. After the oilsoak, it is observed that the formation is open and readily capableoftaking fluid.

While particular embodiments of the invention have been described, itwill be understood, of course, that the invention is not limited theretosince many obvious modifications can be made. and it is intended toinclude within this invention any such modifications as will fall withinthe scope of the claims.

The invention having thus been described, we claim:

1. A method of treating low-temperature subterranean formationspenetrated by a well bore comprising injecting through said well boreand into contact with said formation a liquid having suspended thereindiscrete slowly oil-soluble, water-insoluble, solid particles comprisedof a homogeneous mixture of (1) about 10 to 13 weight percent of anethylenevinyl acetate copolymer that contains about 23 to 30 weightpercent vinyl acetate and exhibits a melt index of about 30 to 500 gramsper 10 minutes and (2) paraffin wax that contains at least 70 weightpercent hydrocarbons having 25 to 32 carbon atoms per molecule.

2. The method defined in claim 1 wherein said ethylenevinyl acetatecopolymer contains about 24 to 26 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule.

3. The method defined in claim I wherein said ethylene vinyl acetatecopolymer contains about 27 to 29 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule.

4. The method defined in claim 1 wherein the temperature of saidformation is less than about I 25 F.

5. The method of completing a well drilled into a permeable,low-temperature, subterranean formation which comprises circulating acompletion fluid from the surface to a drilling zone in said formationduring the drilling operation and returning to the surface at least aportion of said fluid, said completion fluid comprising a liquid havingsuspended therein discrete slowly oil-soluble, water-insoluble, solidparticles comprised of a homogeneous mixture of (I) about 10 to 13weight percent of an ethylene-vinyl acetate copolymer that containsabout 23 to 30 weight percent vinyl acetate and exhibits a melt index ofabout 300 to 500 grams per 10 minutes and 2) parafin wax that containsat least 70 weight percent hydrocarbons having 25 to 32 carbon atoms permolecule.

6. The method defined in claim wherein said ethylenevinyl acetatecopolymer contains about 24 to 26 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per minutes, and whereinsaid parafi'in wax contains at least 90 weight percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.

7. The method defined in claim 5 wherein said ethylenevinyl acetatecopolymer contains between about 27 to 29 weight percent vinyl acetateand exhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.

8. The method defined in claim 5 wherein the temperature of saidformation is less than about 125 F.

9. A method of fracturing a permeable, low-temperature subterraneanformation penetrated by a well which comprises injecting a fracturingfluid into said well and into contact with said fonnation at a pressureand volumetric flow rate sufficient to fracture said formation, saidfracturing fluid comprising a liquid having suspended therein discreteoil-soluble, water-insoluble, solid particles of a homogeneous mixtureof (1) about 10 to 13 weight percent of an ethylene-vinyl acetatecopolymer that contains about 23 to 30 weight percent vinyl acetate andthat exhibits a melt index of about 300 to 500 grams per 10 minutes and(2) paraffin wax that contains at least 70 weight percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.

10. The method defined in claim 9 wherein said ethylenevinyl acetatecopolymer contains about 24 to 26 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per l0 minutes, andwherein said paraffin wax contains at least weight percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.

11. The method defined in claim 9 wherein said ethylenevinyl acetatecopolymer contains about 27 to 29 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per [0 minutes, andwherein said paraffin wax contains at least 90 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule.

12. The method defined in claim 9 wherein the temperature of saidformation is less than about F.

13. A well-treating composition comprising discrete solid particles of ahomogeneous mixture of (1) about 10 to l3 weight percent of anethylene-vinyl acetate copolymer that contains about 23 to 30 weightpercent vinyl acetate and exhibits a melt index of about 300 to 500grams per 10 minutes and (2) paraffin wax that contains at least 70weight percent hydrocarbons having 25 to 32 carbon atoms per molecule.

14. The composition defined in claim 13 wherein said wax contains atleast 90 weight percent hydrocarbons having 25 to 32 carbon atoms permolecule.

15. The composition defined in claim 13 wherein said ethylene-vinylacetate copolymer contains about 24 to 26 weight percent vinyl acetateand exhibits a melt index of about 335 to 465 grams per 10 minutes.

16. The composition defined in claim 13 wherein said ethylene-vinylacetate copolymer contains about 27 to 29 weight percent vinyl acetateand exhibits a melt index of about 335 to 465 grams per 10 minutes.

17. The composition defined in claim 13 wherein said discrete particleshave a mean diameter within the range of about 1 micron to aboutone-half inch.

18. A well-treating composition comprising discrete solid particles of ahomogeneous mixture of (l) about 10 to l3 weight percent of anethylene-vinyl acetate copolymer that contains about 24 to 26 weightpercent vinyl acetate and that exhibits a melt index of about 335 to 465grams per 10 minutes and (2) a fully refined crystalline paraffin waxthat contains at least 90 weight percent hydrocarbons having 25 to 32carbon atoms per molecule.

19. A well-treating composition comprising discrete solid particles of ahomogeneous mixture of (I) about 10 to 13 weight percent of anethylene-vinyl acetate copolymer that contains about 27 to 29 weightpercent vinyl acetate and exhibits a melt index of about 335 to 465grams per 10 minutes and (2) a fully refined, crystalline paraffin waxthat contains at least 90 weight percent hydrocarbons having about 25 to32 carbon atoms per molecule.

EDWARD M.FLETCHEH, JR. Attesting Officer UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patient N00 3 593 79 4 Dated July 20 1971Inventofls) Paul W. Fischer and John W. Scheffel IL is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Claim 1, column 8, line 68 30 should be "300".

Signed and soalod this 11th day of January 1972.

(SEAL) 2 Attest:

ROBERT GO'I'TSCHALK Acting Commissioner of Patents

2. The method defined in claim 1 wherein said ethylene-vinyl acetatecopolymer contains about 24 to 26 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule.
 3. The methoddefined in claim 1 wherein said ethylene-vinyl acetate copolymercontains about 27 to 29 weight percent vinyl acetate and exhibits a meltindex of about 335 to 465 grams per 10 minutes, and wherein saidparaffin wax contains at least 90 weight percent hydrocarbons having 25to 32 carbon atoms per molecule.
 4. The method defined in claim 1wherein the temperature of said formation is less than about 125* F. 5.The method of completing a well drilled into a permeable,low-temperature, subterranean formation which comprises circulating acompletion fluid from the surface to a drilling zone in said formationduring the drilling operation and returning to the surface at least aportion of said fluid, said completion fluid comprising a liquid havingsuspended therein discrete slowly oil-soluble, water-insoluble, solidparticles comprised of a homogeneous mixture of (1) about 10 to 13weight percent of an ethylene-vinyl acetate copolymer that containsabout 23 to 30 weight percent vinyl acetate and exhibits a melt index ofabout 300 to 500 grams per 10 minutes and (2) parafin wax that containsat least 70 weight percent hydrocarbons having 25 to 32 carbon atoms permolecule.
 6. The method defined in claim 5 wherein said ethylene-vinylacetate copolymer contains about 24 to 26 weight percent vinyl acetateand exhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule.
 7. The methoddefined in claim 5 wherein said ethylene-vinyl acetate copolymercontains between about 27 to 29 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.
 8. The method defined inclaim 5 wherein the temperature of said formation is less than about125* F.
 9. A method of fracturing a permeable, low-temperaturesubterranean formation penetrated by a well which comprises injecting afracturing fluid into said well and into contact with said formation ata pressure and volumetric flow rate sufficient to fracture saidformation, said fracturing fluid comprising a liquid having suspendedtherein discrete oil-soluble, water-insoluble, solid particles of ahomogeneous mixture of (1) about 10 to 13 weight percent of anethylene-vinyl acetate copolymer that contains about 23 to 30 weightpercent vinyl acetate and that exhibits a melt index of about 300 to 500gramS per 10 minutes and (2) paraffin wax that contains at least 70weight percent hydrocarbons having 25 to 32 carbon atoms per molecule.10. The method defined in claim 9 wherein said ethylene-vinyl acetatecopolymer contains about 24 to 26 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes, andwherein said paraffin wax contains at least 90 weight percenthydrocarbons having 25 to 32 carbon atoms per molecule.
 11. The methoddefined in claim 9 wherein said ethylene-vinyl acetate copolymercontains about 27 to 29 weight percent vinyl acetate and exhibits a meltindex of about 335 to 465 grams per 10 minutes, and wherein saidparaffin wax contains at least 90 weight percent hydrocarbons having 25to 32 carbon atoms per molecule.
 12. The method defined in claim 9wherein the temperature of said formation is less than about 125* F. 13.A well-treating composition comprising discrete solid particles of ahomogeneous mixture of (1) about 10 to 13 weight percent of anethylene-vinyl acetate copolymer that contains about 23 to 30 weightpercent vinyl acetate and exhibits a melt index of about 300 to 500grams per 10 minutes and (2) paraffin wax that contains at least 70weight percent hydrocarbons having 25 to 32 carbon atoms per molecule.14. The composition defined in claim 13 wherein said wax contains atleast 90 weight percent hydrocarbons having 25 to 32 carbon atoms permolecule.
 15. The composition defined in claim 13 wherein saidethylene-vinyl acetate copolymer contains about 24 to 26 weight percentvinyl acetate and exhibits a melt index of about 335 to 465 grams per 10minutes.
 16. The composition defined in claim 13 wherein saidethylene-vinyl acetate copolymer contains about 27 to 29 weight percentvinyl acetate and exhibits a melt index of about 335 to 465 grams per 10minutes.
 17. The composition defined in claim 13 wherein said discreteparticles have a mean diameter within the range of about 1 micron toabout one-half inch.
 18. A well-treating composition comprising discretesolid particles of a homogeneous mixture of (1) about 10 to 13 weightpercent of an ethylene-vinyl acetate copolymer that contains about 24 to26 weight percent vinyl acetate and that exhibits a melt index of about335 to 465 grams per 10 minutes and (2) a fully refined crystallineparaffin wax that contains at least 90 weight percent hydrocarbonshaving 25 to 32 carbon atoms per molecule.
 19. A well-treatingcomposition comprising discrete solid particles of a homogeneous mixtureof (1) about 10 to 13 weight percent of an ethylene-vinyl acetatecopolymer that contains about 27 to 29 weight percent vinyl acetate andexhibits a melt index of about 335 to 465 grams per 10 minutes and (2) afully refined, crystalline paraffin wax that contains at least 90 weightpercent hydrocarbons having about 25 to 32 carbon atoms per molecule.